1. Field of Invention
This invention pertains to an optical switch array, that is, a switch array for optical signals, such as those carried by fiber optic cables. More particularly, this invention pertains to a switch array made up of a plurality of optical switches and that routes a plurality of optical input signals to a plurality of optical output connections.
2. Description of the Related Art
Optical signals, like their electrical signal counterparts, travel paths that need to be directed to specific locations and those locations are susceptible to change. Electrical signals pass through switches, or routers, that direct any one of a multitude of inputs to any one of a multitude of outputs. Such electrical switches vary in complexity to simple mechanical switches that make and break electrical connections to more complex electrical switches that use circuitry to route the electrical signals.
Optical switching, or routing, initially was performed by plugging in selected fiber optic cables to selected connectors, thereby forming an optical connection. Various switches have been developed to solve the problem of automating optical switching, or routing.
For example, U.S. Pat. No. 6,522,800, titled “Microstructure switches,” issued to Lucero on Feb. 18, 2003, discloses one embodiment of micro-machined devices of silicon (MEMS). Lucero discloses “a microstructure switch having a main body, a moveable switching element, one or more membranes which connect the moveable switching element to the main body and an actuator which moves the moveable switching element from a first position to a second position. The membranes may be either or both of a primary membrane or a secondary membrane. A primary membrane may be used as a temporary membrane which serves to position the moveable switching element until it is permanently positioned by a secondary membrane, or by an actuator. At this point the temporary membrane is removed.”
U.S. Pat. No. 6,571,030, titled “Optical cross-connect switching system,” issued to Ramaswami, et al., on May 27, 2003, discloses an optical cross-connect switching system that includes micro-machined mirrors and a servo system for directing optical signals to the mirrors. Ramaswami discloses a switch subsystem 110 that includes optical switch matrices 241 and 242 that include multiple arrays 300 of micro-machined mirrors that have a mirrored surface 311 and torsional flexures 320, 330 that enable the mirror 310 to adjust its physical orientation to reflect incoming light signals in any selected direction.
U.S. Pat. No. 5,726,788, titled “Dynamically reconfigurable optical interface device using an optically switched backplane,” issued to Fee, et al., on Mar. 10, 1998, discloses an optical interface device using 1×2 optical switches as a basic building block to build N×M switches. A 1×2 optical switch is a switch having a single optical input that is switched between two optical outputs, and Fee does not disclose any structural details of such a switch. Fee discloses a construction of a 1×4 switch and a 4×4 switch using a plurality of 1×2 switches.
One consideration in constructing and using optical switches, or routers, is the bending radius of the fiber optic cable. Fiber optic cables have a minimum bend radius, which is large relative to the cable diameter. Accordingly, routing of fiber optic cables oftentimes determines the size and layout of fiber optic equipment, which is commonly rack mounted with input and output connections accessible from a front panel. In order to accommodate high density requirements, it is desirable to minimize the size of fiber optic equipment.
It is also desirable to minimize attenuation of the optical signals in optical equipment. A factor that affects attenuation is the dimensional stability of the components in the optical equipment. The optical signal from an fiber optic cable has a small size and small changes in alignment, for example, due to changes in temperature, may cause attenuation of the optical signal. Further, it is desirable to operate optical equipment over a wide temperature range, which is at odds with the desire to minimize attenuation.